A data center may include several racks of computing resources such as servers. The various servers in the datacenter are typically connected to each other through a series of switches. If performing a particular task requires the use of multiple servers, communication may require communicating over a network of several switches.
Communication between servers and racks in data centers is typically carried over copper cables. High-bandwidth copper cables (e.g., cables capable of carrying >10 GHz signals) typically have a high loss per unit length, limiting the length of those cables, which in turn limits the number of racks that can be directly connected to a single switch.